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3 marily one oi the noise detecting and evaluating units that are incorporated in a. receiver selection system in accordance with the invention;

Fig. 3 is a schematic circuit diagram illustrating primarily one of the longitudinal balancing units thatmay hawdin a saleotingmiem in accordance :gith the insertion lor mun; the eilect of induced longitudinal noise currents on the merit indicating signal;

Fig. 4 is a schematic circuit diagram illustrating primarily a signal comparison and selecting circuit in accordance with the invention. for comparing the noise or merit indicating signals from the various message lkw receivers. and lor connecting to a utilization circuitiibe mivar output that is associated with the most dirable noise indicating signal;

Fig. 5 is an explanatory graph to which reference is made in the circuit description; and

Pig.6showshowFigs.2.3and4maybear ranged in; disclose, the complete circuit ot one brauch of a selecting which is arranged in with` the invention.

Gomroldsecriptio timwinvolvsastwastmorbe to choose from among any reasonable nnmhar oi such message receivers. Reterring to Fis. 1, the ma message lignei waves are received on the fseparated antennas il. il'. il". and ll". Each of these antennas is osnnected in a radio receiver n.11'. i2". and IZ'". respeotivala. which receivers are substantially alike and may be adapted i'or the reception of umeoiits.. ctaatiailyoi the leveloi itareceived radio frequency signal waves. if the energy level II" at any instant. if'tiie received radio frequency signals exceed this minimum levd. Niiise interference energy that may be received etc. will be added to or includedin the received message signal and such interference energy will bemore prominentin the receiver output productasitsratiototheaudiofrcuuencymessage signal energy in the receiver output is increased. udio frequency output or each receiver i2. Il'. etc. is divided. and one portion of this ener!! from each receiver is tr over oonnectionrfl', il'. ete. to e control terminal or selecting point, where it may be connectedbya reeciverselector il to a utilization circuit II. 'lhesecond portion of this output energy is suppcd to s respective noise detector It, II', ete. MTH-preferably' situated at the same locatector 2l operates on this portion of the output energy to extract from it only the noise ener gies that exist in the frequency spectrum immediately above and below, but not within, the message signal band. It has been determined that in general. the amount ot noise in the voice frequeneyband ofintettis closely relatedto the amount oi noise which occurs above and belaw that band. A measure of these latter quantities is therefore an indirect but satisfactory measure ot noise in the message signal band of interest. This extracted energy is then weighted in a manner which will presently be described before it is used to derive a unidirectional signal. the amplitude of which is indicative of the weiahted. amount of noise encountered in the previously mentioned portions of the frequency spectrum. The amplitude of this unidirectional signal itrelated to the amount of extracted noise energy. and in this described embodiment, it varies in. inverse relation to the amount oi this noise energy. It should be appreciated that this inverse relation between the amount of extracted noise and the amplitude oi the derived signal need not necessarily be followedl and it should not be construed to be a limitation upon the invention. These unidirectional merit indieating voltage signals from the noise detectors 2l.. 2l'. etc. are transmitted to the control terminal. or selection point. over connections 22. 22'. etc. For general descriptive purposes. these connections 22. 22'. etc. are shown as being sep arate from connections Il, Il'. etc. However. aswillbelaterdcribedinconnectionwith Figs., the paired connections il. 22 or il'. 12. ein. may actually consist of a conductor pair.

The control terminal, or selection point, will generally be. but need not necessarily be. geographically separated from the location of receivers i2 and noise detectors 20. The unidirectional merit indicating signal from each noise detector 2| is received by a respective longitudinal balancing unit 2l, 2l. etc. at the control terminai. ln this unit. the Signal is converted from a balanced-toeground signal to a single-ended or unbalanced sig-nal. and any longitudinal noise currents which may have been added toit in the connecting path i! are eil'ectively eliminated.' The signal output of each longitudinal balancing unit Il, M'. etc. consists of a unidirectional voltage, which hasst any instant an amplitude that is representative of the weighted amount of noise energy that accompanies the audio frequency message signal energy in the output circuit of a respective receiver. Since, as was previously stated. the signal energy in the output of each receiver is at any instant at the same level, it follows that a comparison oi the noise energy indications, or merit indicating signals. for the receivers is in enact a comparison of the signal-tonoise ratio of the respective receivers. This tive function is performed in receiver selector iii at the control terminal. For general descriptive this unit is functionally indicated in Fig. i as a mechanical switch arrangement comprising the main contactor l! and switches It. 2l. 28", etc. In addition. o Gu'eshoid circuit 30 and threshold switch $2 are functionally shown as entities separate from the receiver selector It. Actually, as will be noted in connection with the description or Fig. 4. these latter umts may form a portion of the receiver selector II. Selector I6 is arranged such that it responds to the merit indicating unitionasitsradioreceiveritihetc. Noisette-'7s directionalvoltageoflxreatestamplitudes;rg

quentin. The-output of this ampliiler is conmctedthmughah-andormer el toaiuli wave rectiiier. circuit comprising a doubleA diode 12. terminating resista'a 1I. 1| and load resistor 1I. Iheoputotthrectiiiarispassedthroughan energy storage and `titer'arrangement compris. ins iced-resistor 1l, a capacitor 14, and the refcapacitor combination 1t, 11. The time constanten! the rectider and storage circuits are chosensuchthatanniietimeisrequlred forthe cnciwoontained in sudden sharp bursts of noise to dcvelopfull potential across capacitor 1e. In one tested embodiment. a suitable time constant for this circuit was found to be about 100 microseconds. After a potential has been developed across capacity 14 by a surge ot energy, this con denser will dischrsepartly through resistor IS and partly through the resistor-capacitor combinatinn 1t. 11. Thu latter combination forms a nlter circuit which prevents undesirably sudden chang of potential from accumulating across capacitor 11. The discharge time constant of capacitor 1t is preferably relatively long with respect toits charging time constant, and in one .tested embodiment of the invention a dis ohargetime of about milliseconds was found tobesatisioctory. The successful practice of the invention is. of course, not limited to the use, oi the above-mentioned time constants Any other suitable time constants may be used with equal facility. In general. it is believed that therelatlonship of the charging and disoharsins rates should be correlated with limiting factors in other portions ofthe communication system; for example, such factors as the cut-oi! characteristics o! the signal channel,

" andthe response of.,cr appreciation period, of

a limiting unit inthe utilization procese.y In an aural communication system. wherein the highest ,frequency ofthe message signal is restrictedto some deilnite value. and in which some element. such. as the ear. has a fairly definite minimum appremation period; it might be desirable to restrict-the cha-rains period to a value suitably less ythan one-halt tbe cyclic period ofthe highest usable Bienal trecuency. and to arrengethe diechargefperiod at a value suitrindo! the ear. 8mb an arrangement imparts to the detected interference components a weighting factor that is variable with frequency. and, which causes the control effect o! these detected components to vary in a manner that is similar to that in which the impairment effect of mise components is observed to vary in the utilization circuit. At the same time. the response of the detection device is iast enough to permit the proper evaluation. or appreciation. of undesirable quantities of interference energyinashorterperiod thanisrequired by the limiting receptive mmnber for a similar ap praiml. Ihc control electrode of pentode t0 is connected to the common point of resistorcapacitor combination 18, 11. The cathode cir cuitofpentodellincludesenadiustablereaie tor t2 and the potentiometer Il. acroas which areoonnectedcondnctorslltl. Anodcpower supplyforpentodeeeiasecurcdrromther.

spective longitudinal balancing circuit 2l (Mg. 3) at the control terminal point or site. This potentialistranlmlttedtothclocationotnoise detector Il over the upper conductor oi con. ductor pair u. The lower conductor of conductor pair 33 forms the return path for this circuit and is connected to the anode-cathodc circuit of pentode Il at the lower end of cathode load potentiometer 8l. Capacitor It loins the upper and lower sections of the secondary winding o! transformer 3| to form a conductive path for the voice frequency signal currents from receiver I2. and to block the direct current that is flowing in the upper and lower conductors of pair 33.

A similar blocking function ls performed by capacitor |0| at the longitudinal balancim unit end of conductor pair 38, as is shown in lig. 3. Transformer |00 il inserted in the circuit of conductor pair 38, and, together with capacitor loi. forms a blocking circuit for the direct current derived from potential source |20 through resistor |02. The anodeca.thode circuit of pentode In (Fig. 2) includes potential source III, load resistor |02, the upper mnductor of conductor pair u. resistors 8l, Il. the lower conductor oi' conductor pair 8l, resistor I, a portion of voltage dividing potentiometer IM to the grounded terminal of source |20.

Voltage dividing potentiometer |04 provides a convenient and ready means of adjusting the potential of the cathode of pentode 8l. This potentiometer provides a means for imparting a small iixed adjustment to the unidirectional signal voltage as it is obtained from the noise detector Il, and permits the proper coordina tion of these voltages from the various nome detector units of a selecting system. Resistors |02 and |03 may be approximately equal and o! any suitable value consistent with the length of conductor pair 83 and the characteristics of pentode 80.

With respect now to the longitudinal currents balancing circuit or unit 2t, anode potential tor balancing electron discharge device or pentode itt is supplied irom potential source |20 through anode load resistor Ill. Resistors |06, |08, potentiometer |01 and anode load resistor lll form a voltage dividing circuit. The movable arm of potentiometer |01 is connected through a cou- Pu mi' lll t0 the 608ml Blectrode 0fV pentcde lll. Vaima tor these componmte and the the dynamic characteristic oi pentode itl arecoordinatedeucbtbattheameuntotvoltan pe- 1l oharuretliltisepuliedtothecmtnulsridcspap 11 -lidw ill.. iltwil als inqiou. The perdon of et the' receiver is curtailed-bythe level ci modu- Ylatiinst the tsanllutterrthe noise energy in the .ie second portion ot-thesisnaloutput from reiver il is supplied over conductor It to the frequency sensitive networkcomprising capacitor Il and resitos' te and voltage dividing resisten 42, u. netwerkvaries ftnvselywith frequency. 'me networt'hss two routput circuits, ene'o( which is eonnededto the -eeeisapplied overeondunes'stl, Il to thevsris- 'ble loss circuit comm varntoxs H. le, and tm'ds tooontroi theiossthromh this'oiscuitby ,ecntroiiingthemmedanceserthevastsmrn The -secid output from the` ii'equenc! smsitive network, Il is uniud over emduetlt to theV l2 o! .the limiting action in receiver Il, less ndse energy will now ybe rectined than was previously the cese, and the potential across capacitor-'11 will be reduced. The negative potential at the `cositrolgrid electrode oi' pentode l0 will now be isssthaninourpreviouslyassumedcase. where no message signal was being received. The

amde-cathode current in this pentode will now vlie-increased. and will provide a greater voltage across potentiometer I4 than heretofore existed. The potentials that are generated acro this potentiometer by the passage through it of cathode-current i'rom pentode 80 and the rectiiied current trom rectier el are opposed in polarity. no net potentiel is supplied over conductors ll.- 64 to the previously-mentioned variable las circuit comprising varisters 52, 56 where it controis the transmission loss through this circuit by the characteristic of these variatore.

The action oi this feedback arrangement h to -linearize the relationship between the currmt ilewinginthesnodo-cathede circuitofpentode Il. with respect to logarithmic variations in the level of tlm noise input to detector 20. Tlus gg. action comes about because the magnitude oi the 'ebb Bom the more desirable logarithmic char anodecathode curxentoipentode le isaninvene function ot the level oi the rectiiied noise energy.

-As the noise level is decreased. the cathode cui'- rent ot pentodeand the potential across petentinmeter I4 are increased. This increased voltage is fed back over conductors B2, M to the variable inse circuit where it decreases the transmission loss by controlling the characteristics of variatore '52, it. This laction tends to increase therectied noise energy, and thereby reduce theoathode current oi pentode 0l, and the potential across potentiometer it. The net elect oi' this arrangement is to produce a stabilized Usteni having the desired characteristic. such as isshovm bytheidealizedcurve |12 of Fig.5.

-Gutvei'llshowsthemannerinwhichtheanodecathode current in pentode It may be changed by logaritinnicvariationsin the level o! the noise energy that is applied to the input of detector-II .whensumoientvoltaeois ted backtocontrol varistors l2. 6I possessing suitable current-voltagceheraoieristics. It no feedback arrangement. or its equivalent. were used the input-output dissecteristio oi detector It would be similar to that shown by curve |14 of this figure. It will he noted that this latter curve varies consideracteristie and that its operation is restricted toa relatively small range of input levels. The departure may be great enough that signals having a suitable or acceptable noise ratio would be rejected. Prom the described action of detector 2l, it willv be appreciated that this unit produces in its anode-cathode circuit, and, therefore, in the direct current circuit which includes conductor pair It. a current the magnitude oi' which increases linearly as the logarithmic relation between the dgnal and noise in the output ot receiver Il h increased. Therefore, for low noise values this current will be et its maximum values. Potentmmeter Il is made adjustable to permit Vcontrol oi the amount ot this ied back voltage so that omentinlly the saine input-output charactexistic ma! be obtained from each noise detector il in the lecidng system.

'Became non-linearity generally exists in the transmission path between the input to a radio uansmitter and the signal output of its associated receiver, there results a distortion product ehieescapacitorsn." anoresbtor ie. A.leceuseurproductswhenever-.a message lisnaiis trsssbyany one dtbeother receivers It'. i2" .or |i'". Relay iseeonnects ground over its contact,'through thelinding of threshold relay |00. topotentialseueee I'Illsndcausesthislstter Isndolcsestheeontactllmdtofthis remainder of the receivers are rejected selecticnbnnch of selector it will now toinoresse its'anode-cathode current to s value that is sumcieni to spente relay |88. Relay iltconnectsgromlioveritscontacttothewinding of relay' |02. The operation of relay |02 operi the shortmuiting connection across re- ..25

sister |52, provided by normally closed contact Iofrelay |02, sndclosesoveritseontaetsi and t the connection iromcoudnctor pair n to interemnscting pair ill. elnce pair Mt is closed through contacts 5 and t of relay i to the zo -utimation circuitfll, the output of receiver i2 is connected to thislsttercircuit.

Itwillbsnotedthstresistor itlisincladedin the cathode circuit-od each triode i, iu', ete.

The voltage that il developed' across this resistor z5 'bythe combined curreutilowin all tricdes I,

ltl'fetc. exerts 'a degenerative feed-back eect which tends'to Nuthe cathode o! each tube ed any other triade, the current ow`throu8h 45 ythe triode having'the highest potential on its control electrode will establish the potential at I, and the remainder 0f the trim III', tu",

etc. will cease conduction. This condition will continue until some one oi tim hnsltlldlnai balancingunits 2l', il" ein. supplies toits associated eo selector It mighteonnect the output of two rees ceivers, for example, receiver I2 and l2' to the utilisation circuit il, or it might be subjected to undesirable indecision by switching from' the outmtoieneto'thstotanotherofthereceivers asthenoiseenergyinthe output circlnts oithese 70 receiversnuctuatesoneabovetheotherbya slight amoimt. l To prevent these conditions. a preierential hissing errer-moment is provided suchthatwhena-usabissignallnsbeenehosen .be seleetorilritwilloontimseto beehosennntil 16 operate.1hich aetim opens contacts es manner in. which receiver I2 is selectedfio 16 itisswplantedbysmoredesirablesisnalwhich exceeds the chosen signal by a predetermined amount. This preferential biasing feature is brought into action when relay |42 opens the circuit which was formerly closed over its contact l. This action removes the short-circuit connection which formerly existed across resistor |52, and produces across the combined resistors III, Il! s. voltage drop which is equal to the potential of source IN. The eiiect of this action is to lower the potential of the cathode electrode of triode I with respect to the potential of the remailling cathode electrodes by a predetermined amount which is controlled by the relative values o! resistor ill, |52 and the potential of source |54. Under these circumstances then, before any other branch of selector it can connect the output of its associated receiver to utilization circuit Il, andinsodoing bias triode |34 ofthe upper branch to its non-conduction state, the potential on the control grid electrode of its associated discharge device must exceed the potential on the control grid electrode of triode I by at least the amount of the voltage drop across resistor |52.

Each electron discharge device or vacuum tube |34, |30', etc., of the selector tube array is preferably chosen for a high transconductanoe wherein a relatively small change in grid-cathode potential diil'erence will produce a relatively large change in anode-cathode circuit current. As already referred to hereinabove, the circuits associated with the electrodes of these tubes include feedback by virtue of the common cathode resistor llt, to establish an anode-cathode current in that one of the tube array whose control grid has received the highest-valued input signal. that is. input signal respective the best meritindicating signal. This anode-cathode current remains substantially constant even though the potential applied to the control grid of such one tube varies or changes over a range corresponding to a wide variation of input; assuming, of course, that the range of variation of the potential applied to the control grids of the other tubes during such period is at all times less than the then applied potential on the control grid of the one tube, taking into consideration, also, the preferential bias provided by the resistor Ill, |52', etc. However, when the control grid potential on one of the other tubes is such that current is caused to ilow in the anode-cathode circuit of such second tube, then a small variation in the potential of either such one tube or such second tube produces large changes of current in their respective anode-cathode circuits. In a tested embodiment of such a tube array, the devices |84, |34', etc. were R. C. A. type GSL'ICYI': the resistor I was of 100,000 ohms; resistors Ill, ill', etc., and resistors |52, |52', etc., were of 1000 ohms each; the relays |38, |38', etc., were chosen and adjusted for operation on approximately .7 milliampa'e and for release on approximately .4 milliampere; cathode-anode circuit current through the cathode resistor |46 varied between approximately 1.5 and 1.9 milliamperes.

For descriptive purposes. let it now be assumed that there is received on conductors |22'" and |24'", a signal having an amplitude that is greaterthan that of the signal on conductors |12, |20 by more than the voltage drop across resister |52. The main anode-cathode conduction path will be transferred from the upper selection branch, which includes triode |34, to the lower selection branch, which includes triade mamen vidualtoeechotceidreceivingchnnnellforcllf tinuously deriving c. quantitative electric m u sentation of the ncile nve component: che andbeiowhutnct'ithinthebcndotseid'dllll frequenciesinthesspective chcnneLthcmssnitude of seid representation chansing suhetsnv tieiiy in lonrithmic relation to changes in tl megnitudeofsuidnoiseweve compcnents,mesnc for comparing seid quantitative representation and connecting means-lor interconnecting seid oommonspeechwlvechlnnelnndonlythctcltf ofsaidreceivingchsnncisimmwhiohthelee quantitative repnsentotionisohteineicoidlle pcrisonmecnsbeinsedeptedtooontroltheopy eration of seid connecting means. f 8. In a. communication sz'tem cofmprisiN- menercieeinthocutoutcimutotnm phxnlityoi ancor-convey;

vgxecsim,m4mmmnbmh ingthesuneimmiofnuciioirequeucyelectrieAv derived for lewaves lndtheirsocompnnyingnoisecomponeng'. j :new www@ gm un n.- 2 a common audio frequency wave chennel. und

nclreoeiverthstcroducesthederivedmncf mcenstorinteroonnectingsnyoneotseidh'anlueetestmneniindmaidselectingmecnsoomi missionpethsandnidoommonchanneLmeg! msingeneiecirondiachcreodevieereenective .l'lpectivecechofsoicixauthcforrierivineiecbioV eechreooivercndincludingetleutonnnode.; veveenerzytromthenoisewevecomponenildf f cathodeandeccntrclmdelecundggmqo-frequencimthercnzelyaboveendbelowcethcdeondcontxolsrid-thodecircuibthere- WOIQIMWOWOMUMHM ionswitchingmeeneresnectiveeechctaoiddoand means included in scid interconnecting remonlivetccurrentiiowinginthe mlndriwneinblliddl'ivedmrlyf:

snode-cathodexoincuitotseid devices iorconnecte interconnecting with` seid common channel, A .inetosutilintionarcumnacutpnccrmm- 3 them11110110fthwtlwrwif-hetnetrespective4 mlilnhlveoeivenmimhnonedcsm mithilxvomwhichtheieectnoiseenna-fryingA cirum fi f cuitoieochoiniddevimmdmeonsiordisg-mmmmummmmpml conneotingnognssidummmmgmoug. pluralityotpcthseochtoroonvq.

.A thedgnvcduinogtheumehendoteudiofrequencyelectu d man' in umn of Mmmm man: common audio frequency xrveechon; u" relum nel. cmi means for in any one receiving chlnneiseechto'r conveying m nel. means resnectiveeechot said paths for cneeohnvelnndtheirsccomnmyinznouieeweve w um 19cm n" m mm the n1 ""9 t componenuespeechwevechennelior tfmmmthmem 1 ,withoenyone oiceidreoeiving mvemdm'mtmmwdmd W ,Mw am, ,um fregi gn' amm" 01mm ""1 th o au requency waves or ma www onlvshtgslcn; 5 Mint tlremmnlimmontredwvelultc belcvl the cccnpenying speech' waves. ond mm man. .means derived electric energy when u um my lm Y w :or vingcnmmrrom mmwllvhlvhleveimdmeamincl In.; dgm'm um' said interconnecting means and responsivev I. um 5 seldderivedenergyiorinterconnectingwith commonchnnneLtothcexclusionotthe peths.thctrespectivepethfromwhichthe l noiseencrgyiscoderived. 'J l 10. Acommunicctionixystemcoxnpriixingcphp` .s

55 raiity of path; eech for conveying sudiofreliilencymellexelilnnisond sccompenyint noieewlve te, means respective cif- ,eecixnothiderivingtromsuchwoveenergy f o theirequencyrenceomyeboveondheiowthst l 00 themessage sisneienlexit indicatinc demkq' vaahie'ohcrncterictic of which is indicative "y in the relative level o! the 'eimilcndeceomponyingnoiseotthe jf tive path, a utiiilntion circuit for interconnec- 66 tionwitixenyoncotseiclpinthmencimeenlil cponsivetocoidcherocteristicofeechofll for interconnecting with seid'u lisation circuit that one of seid mths having hetterreistiveievei ofmelsege ciencia emile 10 compenvinz noise.

iiJlhecn system of claim 10 in which addiert-mentioned means comprises o 'l plurality of nid-continued electron dilehsxp Y devieechnving anode-cathode circuitmeechdY onyoneotscid'lncehinlehnnneinmennsindi- 'whiehincludesoioedreeistortorhill .Iwan

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